Process for extracting aromatic hydrocarbons from hydrocarbon mixtures containing same



Jun 13, 1967 E. CINELLI ETAL 3,325,399

PROCESS FOR EXTRACTING AROMATIC HYDROCARBONS FROM? YDROCARBON MIXTURES CONTAINING SAME Filed Oct. 7, 1965 INVENTORS HAM/W0 cu/nu a! P/ERww/E G/RaTT/ United States Patent 3,325,399 PROCESS FOR EXTRACTING AROMATIC HY DRO- CARBONS FROM HYDROCARBON MIXTURES CONTAINING SAME Ermanno Cinelli and Pierleone Girotti, San Donato Milanese, Milan, Italy, assignors to Snam S.p.A., Milan, Italy, a company of Italy Filed Oct. 7, 1965, Ser. No. 493,850 Claims priority, application Italy, Oct. 14, 1964, 22,059/64, Patent 737,788 Claims. '(Cl. 208-321) This invention relates to a process for the separation of aromatic hydrocarbons from hydrocarbonaceous mixtures by solvent extraction, which is eflicient both in the treatment of low-boiling and of high-boiling hydrocarbonaceous fractions.

The prior art disclosed many processes for the ext-raction with solvent of aromatic hydrocarbons from hydrocarbonaceous fractions. According to these processes, the extract consisting of the solvent and the aromatic hydrocarbon contained therein is distilled so as to regenerate the solvent while recovering the aromatic compound.

These processes prove to be eflicient only so long as the boiling point of the solvent is notably different from the boiling point of the hydrocarbon contained in the extract, but cannot be readily applied when the boiling points of the solvent and of the hydrocarbon, respectively, are near to one another.

An object of the present invention is to provide a process for the extraction of aromatic hydrocarbons which can be readily applied even when the boiling points of the hydrocarbons and of the solvent present in the extract are near to one another.

Inasmuch as in the extract the maximum concentration which can be obtained, in terms of aromatic hydrocarbons, from the hydrocarbonaceous fraction contained in the extract is given, in the triangular plot solvent-aromatics-nonaromatics, by the tangent to the binodal curve passing through the solvent apex, and inasmuch as said concentration is not suflicient, in general, to give a sufficiently pure aromatic product, it is necessary to adopt various modes of operation in order that the purity of the extracted aromatic fraction be increased. It is possible, for example, to modify the characteristics of the solvent by adding thereto substances which, like water, modify the triangular plot aforesaid so as to make the solvent more selective; it is also possible so to modify the triangular plot so as to convert it into an open plot, i.e. of a kind in which a reflux of aromatics contributes towards an improvement of the purity of the final extract. Refluxes from the side of the extract of a low-boiling non-aromatic component are also known, said component being more soluble, in the solvent, than the nonaromatics having a higher boiling point. Said refluxes remove -from the extract the non-aromatic hydrocarbons having the higher boiling points and replace the latter, whereafter they can be easily separated from the aromatics extracted by distillation, owing to the notable difference between the respective boiling points. The necessity of said operations for extracting adequately pure aromatics imposes therefore expensive processing runs.

Distillation of the extract, the presence of water, even in large amounts, in the solvent and which is distilled off from the extract and is to be recycled, along with the particularly 4-formylmorphoexhibits, either alone or admixed with water, solvent properties for the aromatics, which are fully satisfactory as far as transferring power and selectivity are concerned.

An inherent drawback shown by these solvents and, more particularly, by formylmorpholine, is its corrosive power, along with the extremely low stability at temperatures over 90 0, especially if water is present.

Still more particularly, formylmorpholine, both in its anhydrous and hydrated form, exhibits a corrosive action towards the conventional materials and is rapidly altered in the presence of ferrous products of the corrosion.

An object of the present invention is to provide a process which uses the satisfactory solvent characteristics of formylmorpholine in spite of the aforementioned shortcomings. It is thus compulsory that formylmorpholine be employed, in each and every stage of the process run, at temperatures under 90 C. The foregoing objects are achieved by a process which comprises the following steps:

Feeding at one end of a counterflow contact system a solvent which essentially consists of formylmorpholine, feeding the stock at one or more intermediate points of said system, feeding a non-aromatic reflux, having a boiling point lower than that of said stock, at the end of the system which is opposite to the solvent feed-in point, distilling off from the refined stock the lightweight fraction coming from the non-aromatic reflux, washing the extract in counter-flow with a non-aromatic hydrocarbonaceous fraction having a boiling point lower than that of the aromatics contained in the extract and discharging, from one side a stream consisting of virtually aromatic-free regenerated solvent and, from the other side, a stream formed by the hydrocarbons retained by the extract and by the non-aromatic hydrocarbonaceous washings.

Said stream is sent to the distillation system to remove the fraction employed for the washing step from the extracted hydrocarbons.

In the processing steps outlined in the foregoing, that is to say, in the steps in which formylmorp'holine is present, the temperature is maintained between 20 C. and 90 C., the 25 C. C. range being preferred, i.e. in the stability and non-corrosiveness field of formylmorpholine.

The treatment of the extracted fraction consists of a distillation of the non-aromatic lightweight fraction which is utilized as the washing and refluxing agent, and of a subsequent distillation, from the tailings of the previous distillation step, of a fraction which is recycled to the extraction as stock and is formed by a fraction of the more volatile hydrocarbon along with the small amount of possibly present non-aromatics. The final product essentially consists of aromatic hydrocarbons.

The transferring power and the selectivity of phenylmorpholine are so favorable the solvent/stock ratio, as well as the amounts and refluxed and recycled fluids are drastically reduced with respect to the prior art methods.

The ratio by volume of the solvent to the fed-in stock ranges between 1 to 1 and 5 to 1, and preferably lies between 2:1 and 3.5: 1. Even with so low values as compared with those of the known methods, it is possible to recover aromatics with yields over 96% and with a nitration grade purity.

The addition of water to formylmorpholine does not display any appreciable effects but improves the selectivity thereof while causing the solvent power to be decreased, as occurs also with the prior art solvents. In practice the process employing hydrated formylmorpholine exhibits the following differences over the process with anhydrous formylmorpholine The solvent to stock ratio is slightly higher, still within the aforementioned range.

The reflux to stock ratio is slightly lower.

A lesser amount of washing fraction is experienced.

More particularly it is fitting to note that, even though the process employs aqueous formylmorpholine, the heat balance of the process is kept unaltered since the water contained in the solvent does not enter distillation steps, as contrasted to the prior art methods. Differently from the known methods, refluxing aromatic hydrocarbons at the extract discharge end would prove not only unprofitable, but even harmful. As a matter of fact, as formylmorpholine has a selectivity which is high enough as to make it unnecessary to resort to water additions in so high amounts as to convert the closed triangular plot solventnonaromatic-aromatic into an open plot, the aromatic reflux would induce in the extract a solubilization of the two phases at the equilibrium at the extract end.

The water reflux, adopted in few processes, is affected, in general, by the shortcoming that one is compelled to distill off from the solvent of the extract the amount of water which appertains to the'refiux and thus, on account of the high latent heat of evaporation of Water (about 540 calories per kg), an increase of heat waste would become compulsory.

The very high selectivity towards aromatics along with the very low solvent power for non-aromatics as shown by formylmorpholine, which on the other hand displays a preferential solubility for the lightweight non-aromatics with respect to the heavier ones, acts in such a way that a reflux of low-boiling non-aromatics, preferably paraflins, is more advisable. It has been found that the volume ratios of non-aromatic refluxes to fresh stock as fed are fit to the purpose according to an unexpectedly low rating, i.e. between 0.15 to 1 and 0.7 to 1; and preferably between 0.25 to 1 and 0.5 to 1.

The more volatile fraction which is distilled off from the solvent-deprived extract, after the separation of the non-aromatic to be used for washing and refluxing, contains a notable aliquot of the more volatile aromatic hydrocarbon along with virtually all the non-aromatic components which were present. Said fraction is not used for refluxing, in that the aromatics which are present would not give rise to an advantage for said operation, but is fed-in at the extraction stage as a stock, i.e. in the stage in which the hydrooarbonaceous fraction which is present has a composition which is near that of the stream to be fed-in, not to trouble the extraction conditions or to cause the undesirable solubilization of the phases at the equilibrium, either.

The usefulness of the separation, from the extract, of a fraction comprising a portion of the more volatile aromatic component along with all the non-aromatics, which generally have a low boiling point, is inherent in the improvement of the final extract and not in the extraction conditions. Said recycled fraction, however, is but a slight fraction of the stock and the effective ratio of said fraction of the fresh stock lies between 0.02 to 1 and 0.2 to 1.

The extract-washing step for recovering, on the one side, the solvent and, on the other side the aromatic hydrocarbons, has proven to have a surprising efficiency; the ratio of the nonaromatic lightweight fraction employed for the washing, to the amount of the solvent introduced at the extraction stage lies between 0.5 to 1 and 1.2 to 1 in order that a virtually total recovery of the aromatic hydrocarbons be obtained. By way of example only, a washing carried out in a system comprised of 6 to 10 stages permits the obtention of a solvent having an aromatics con-tent of less than 1% by weight and a content of non-aromatic lightweight washings of less than 2% by weight.

One of the advantages of the present invention lies in that the extraction of the aromatic fraction and the separate recovery of the solvent and of the hydrocarbon of the extract are carried out without heat waste and with simple implementation. Very satisfactory results are obtained with a few stages of conventional counterflow contact columns.

With the inventive process, formylmorpholine has proven to be extremely stable and noncorrosive and, under these respects, it has proven equal to the conventional solvent fluids.

By way of example, a typical embodiment of the process, as applied to the fractions from C to C will be described with the aid of the accompanying drawing.

An extraction system 1 is charged with the solvent, consisting of anhydrous formylmorpholine, via the conduit 2, with the fresh stock, consisting of a 60 C.- C. aromatic-containing fraction, via the conduit 3, with a recycling feed formed by a C fraction through the conduit 4, with a non-aromatic reflux having a boiling point lower than 60 C. and essentially consisting of a C fraction through the conduit 5. From the top, the refined stock is discharged through the conduit 6 and, from the lower end the extract is discharged via the conduit 7.

The refined stock is then introduced in the washing systern 8 wherein, through the conduit 9, water is fed in. Within said washing system 8, the traces of formylmorpholine contained in the refined stock are removed in the form of a very diluted aqueous solution which is discharged via the conduit 10, whereas the solvent-freed refined stock is forwarded to the conduit 11.

The solvent-free refined stock is sent to the column 12 wherein a fraction, boiling under 60 C., is distilled off the refined stock, i.e. the fraction appertaining to the lowboiling nonaromatic reflux. Said fraction is removed via the conduit 13, whereas the bottoms form the final refined stock which is sent out via the conduit 14.

The extract, discharged with the conduit 7, is introduced in the washing system 15 wherein, via the conduit 16, a lightweight non-aromatic fraction whose boiling point is under 60 C., is also introduced. The two fed-in streams are counterflown with respect to one another with an exchange of materials and two streams are discharged, the lightest one forming the solvent-free extract containing the extracted hydrocarbons and the hydrocarbonaceous washing fraction which is discharged via the conduit 17, the heavier one consisting of formylmorpholine with a small amount of hydrocarbons which is discharged via the conduit 18.

The solvent-free extract is then introduced, via the duct 17, into the washing system 19 wherein the formylmorpholine traces which are possibly present are washed with water having a low content of formylmorpholine which is coming through the conduit 10.

The washing system 19 thus discharges two streams, the

fraction will be, advantageously, a pentane fraction, whereas, if the lowest-boiling aromatic to be extracted were xylene, the non-aromatic fraction to be used for refluxing and washing could be a heptane fraction.

heavier one consisting of water with formylmorpholine In order that the advantages of the invention may apwhich is discharged via the conduit 20', the lighter one, pear fully conspicuous a few examples will be reported formed by the solvent-free extract, which is discharged hereinafter, which are not to be construed as limiting the through the conduit 21. invention in any wise.

Water and formylmorpholine, discharged through the EXAMPLE 1 conduit 20, are introduced in to the column 22.

Said fraction, which is a small amount, is distilled un- The raw ck p y i a catalytic reforming g der proper conditions to recover formylmorpholine, disllne having the following specifications: charged via the conduit 23, and combined in the conduit S ecific ravit at 200 C 570 2 with the stream coming from 1a and Water which, via Rantin s mix ND film the conduit 9, is utilized for the washing step again. Benzene by Weight" The solvent-free extract, from the conduit 21, is lntro- Composition: duced in the column 24 whereln a fractlon-bo llng under Toluene "percent by Weight 17 41 60 C. 1s dlstllled off as a head portlon whlch ls then dls- Xylenes plus ethylbenzene do 23.24 charged via the conduit 25. Sald fractlon ls parted into parafiins do 54 88 two streams, either of which is combined via the conduit 2() A.S.T.M. dlstlllatlon. 26 with the stream coming from the conduit 13 and then Start 0 C 65 through the conduit 5 and is used as a refluxing agent,

1% dlstlls at C 72 the other one being sent through the condult 16 to the syso 5% dlstlls at C 85 tern 15 as a washlng agent. 10% distfls at o C 88 The bottoms of column 24, consisting of aromatic 207 a lstlls at C 90 hydrocarbons extracted from the stock and a small pordistfls at o C 96 tion of non-aromatic, virtually low-boiling hydrocarbons,

dlstlls at C s 100 for which the reflux and the washing fractlon are respono dlstlls at C 106 slble, is fed into the column 28 via the duct 27. distils at o C 112 In said column 28 is distilled a head fraction which, via 3 distils at I, 119 the conduit 4, is sent back to the ex r ion st ge as a disms at "s 126 recycle d consists of a slight non-aromatic fraction 3 dlstlls at C 133 whlch ls present 1n the extract and ln a portlon of the distfls at o C 139 more volatile aromatic hydrocarbon. The bott m pr c End o 144 essentially contains aromatic hydrocar ons nly nd 1s 35 fl; 1 discharged i 29 and sent to an aromatic-fractionation "Percen Recovery do 99 stage (not shown).

Any kind of hydrocarbonaceous stock containing an By employing a process with an anhydrous solvent aromatic fraction can be treated according to the invenslrnllar to that described in the diagram of the accomtive process in order to recover aromatics. 40 panying drawing, wherein the extraction column consists In general petroleum stocks are used for the production of 15 stages and the extract washing column comprises Z of aromatics and more particularly the reforming prodstages, and operating at an extraction and washing temucts which have a notable content of aromatic hydroperature of 25 C., the results tabulated in Table l have carbons. been obtained. The volume ratio as employed, of solvent The inventive process is characterized by its possibility 45 to stock is 2.5 to 1, the employed ratio of light-Weight of being employed for the whole set of aromatic hydro-, non-aromatic washing fraction to solvent is 0.9 to 1; the carbons, from benzene to naphthalene, in that the boiling ratio of refluxing agent to fresh stock is 0.4 to 1; the ratio point of the solvent is immaterial to the end of putting of recycle to fresh stock is 0.1 to 1. the process into actual practice. The refluxing and washing fraction essentially consists While the process is being progressively applied to the 50 of pentane, heavier fractions, also the non-aromatic fraction em- The rates of flow and the compositions shown in Table ployed for refluxing and washing can be displaced towards 1 are by volume and refer, each, to the reference numerals the heavier members: for example, if the lowest boiling of the flow diagram shown in the accompanying drawing, aromatic to be extracted is benzene, the non-aromatic said numerals being shown at the head of the table.

TABLE 1 Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent TABLE 1Continuetl Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Pentane 6.225 2.55 Saturated Hyd 0. 050 0.02 2.175 0.89 0.400 0.16 0.050 0.02 235.370 96.36

Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent P t ne 229.972 82.14 228.972 Saturated Hyd 1. 19 Benzene 12.724 4.54 15.710 5.61 19.750 7.06

It can be seen that the recovery of aromatic hydrocarbons is 96.38% for benzene, 99.41% for toluene, 96.71% for the xylenes, the overall recovery is 97.73%.

EXAMPLE 2 The same stock of the preceding example has been treated with an aqueous solvent, still maintaining a temperature of 25 C. in the extraction and washing stages.

The operative conditions and the result obtained are tabulated in Table 2.

The flow diagram of the process is the same as that of the accompanying drawing, with the only exception that The recovery of aromatic hydrocarbons is 96.40% for benzene, 97.42% for toluene, 94.86% for xylenes, the overall recovery being as high as 96%.

The substantial result of this processing run lies in the lesser amount of hydrocarbons to be distilled in a cycle, a slightly lower yield of aromatics being obtained.

EXAMPLE 3 The raw stock employed is a cut 63 103 C. of a catalytic reforming gasoline having the following specifications:

. o the stream 13 is combined with the stream 16 instead of 40 i ii ig y g at 3 0'7464 being combined to the stream 26 to form the reflux 6 ac 1 n ex 1-4248 stream 5 Benzene "P rcent by Volume 19,00 Toluene do 18 08 The reflux stream 5, therefore, will have the same com- Parafli position of the stream 25. ns 62'92 TABLE 2 Parts Per- Parts Per- Parts Pcr- Parts Per- Parts Per- Parts Per- Parts Percent cent cent cent cent cent t Pentane 5 400 1.80 1.00 Saturated Hyd- 0.000 0.02 60. 41 60. 41 0.20 Benzene. 0 936 0.31 3.87 3.87 8.30 Toluene- 0 780 0.26 15.30 15.30 0.50 Xylenes. 0.624 0. 21 20 42 20.42 Solvent 283.434 94. 48 Water 8. 766 2. 92

Total 300.000 100. 00 100. 00 100. 00 10.00

Parts Per- Parts Per- Parts Pcr- Parts Per- Parts Per- Parts Per- Parts Percent cent cent cent cent cent cent Pentane. 29.340 99.22 148.084 Saturated Hyd. 0 208 0.70 60, 410 9 1.046 Benzene 0 023 0 08 0.139 0.450 Toluene Xylenes" Solvent Water Total 10. 479 100. 00 29. 571

TABLE 2-C011tinued Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Parts Percent Pentane 2.08 Saturated Hyd 0.42 Benzene 25. 06 3. 731 9.82 Toluene 32. 09 14. 905 39. 22 Xylenes 40. 35 19. 371 50. 96 Solvent.

The extraction was carried out at the following operative conditions:

Volume ratio solvent to stock 1.2/ 1 Temperature C 25 Water in solvent mixture percent by weight 3 Volume ratio of aromatic reflux to stock 0.1/1 Volume ratio of nonaromatic reflux to stock 0.3/1 Volume ratio of washing pentane to solvent 1.34/1

The recovery of aromatic hydrocarbons was 96.4% for benzene and 95.2% for toluene, with a complexive purity of 98.59% by volume.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for obtaining aromatic hydrocarbons from mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons by extraction with a solvent, characterized in that it comprises the steps of: introducing the hydrocarbonaceous mixture in an intermediate point of a counterflow extraction system and introducing at one end of said extraction system a solvent essentially consisting of formylmorpholine and, from the opposite end, a refluxing agent essentially consisting of a light paraflin fraction having a boiling point substantially lower than that of the hydrocarbons contained in the hydrocarbonaceous mixture, while maintaining the phases in mutual contact at a temperature between C. and 90 C., discharging a refined stock substantially devoid of aromatic hydrocarbons and of solvent from the same end of the system wherein the solvent is introduced, discharging an extract formed by the solvent, the aromatic hydrocarbons and a portion of the refluxing agent and substantially free of the non-aromatic hydrocarbons fed-in with the hydrocarbonaceous mixture, subjecting the extract thus obtained to washing within a counterflow contact system with a light paraflin fraction having a boiling point definitely lower than that of the aromatic hydrocarbons present in the extract, discharging from the contact system in which the washing is carried out a heavier phase consisting of all the solvent and substantially free of hydrocarbons, and discharging from the opposite end a hydrocarbonaceous phase consisting of the solvent-freed aromatic hydrocarbons extracted from the hydrocarbonaceous mixture and light paraflin hydrocarbons having a boiling point substantially lower than that of the more volatile aromatic hydrocarbon present in the system, separating the extracted aromatic hydrocarbons and light paraflin hydrocarbons having a boiling point substantially lower than that of the more volatile aromatic hydrocarbon present in the system from the solvent-freed extract by evaporation under such conditions as to evolve therefrom a major aliquot of the lowboiling light parafiin fraction which is utilized as a refluxing agent again and as a washing agent, separating thereafter from the residual extract the remainder of the light paraflin fraction along with a portion of the more volatile aromatic hydrocarbon as a stream, mixing said stream obtained with the feed to the extraction system and not as a reflux, and obtaining as a bottom product a hydrocarbonaceous fraction consisting of substantially pure aromatic hydrocarbons the temperature being maintained between 20 C. and C. throughout the whole process.

2. A process according to claim 1, wherein the solvent essentially consists of formylmorpholine containing Water in an amount from 0.5% to 10% by volume.

3. A process according to claim 1, for the extraction of benzene, toluene, xylenes and ethylbenzene from hydrocarbonaceous mixtures containing them, wherein the light paraflin fraction employed for refluxing and washing essentially consists of pentane.

4. A process according to claim 1, for the extraction of benzene, toluene, xylenes and ethylbenzene from hydrocarbonaceous mixtures containing them, wherein the light parafiin fraction employed for refluxing and washing essentially consists of butane.

5. A process according to claim 1, wherein the extraction and the washing are carried out at a pressure sufficient to maintain all of the contacted phases in a condensed condition.

6. A process according to claim 1, wherein the refined stock obtained by extraction is subjected to distillation for separating the light paraflin fraction coming from the refluxing stage and utilizing it as such again.

7. A process according to claim 1, wherein the traces of solvent present in the refined stock and in the solventfreed extract are recovered by washing with water.

8. A process according to claim 1, wherein the volume ratio of the solvent to the fed-in stock is between 1 to 1 and 5 to 1.

9. A process according to claim 11, wherein the volume ratio of the feed stock and the non-aromatic reflux at the extraction stage is between 0.15 to 1 and 0.7 to 1.

10. A process according to claim 1, wherein the ratio by volume of the solvent to the light paraflin fraction employed for washing the extract is between 0.5 to 1 and 1.2 to 1.

References Cited UNITED STATES PATENTS 2,357,667 9/1944 Kuhn 208--326 3,177,196 4/1965 Scheibel 208-317 3,186,937 6/1965 Anderson et al 208-314 DELBERT E. GANTZ, Primary Examiner. HERBERT LEVINE, Examiner. 

1. A PROCESS FOR OBTAINING AROMATIC HYDROCARBONS FROM MIXTURES OF AROMATIC HYDROCARBOINS AND NON-AROMATIC HYDROCARBONS BY EXTRACTION WITH A SOLVENT, CHARACTERIZED IN THAT IT COMPRISES THE STEPS OF: INTRODUCING THE HYDROCARBONACEOUS MIXTURE IN AN INTERMEDIATE POINT OF A COUNTERFLOW EXTRACTION SYSTEM AND INTRODUCING AT ONE END OF SAID EXTRACTION SYSTEM A SOLVENT ESSENTIALLY CONSISTING OF FORMYLMORPHOLINE AND, FROM THE OPPOSITE END, A REFLUXING AGENT ESSENTIALLY CONSISTING OF A LIGHT PARAFFIN FRACTION HAVING A BOILING POINT SUBSTANTIALLY LOWER THAN THAT OF THE HYDROCARBONS CONTAINED IN THE HYDROCARBONACEOUS MIXTURE, WHILE MAINTAINING THE PHASES IN MUTUAL CONTACT AT A TEMPERATURE BETWEEN 20*C. AND 90*C., DISCHARGING A REFINED STOCK SUBSTANTIALLY DEVOID OF AROMATIC HYDROCARBONS AND OF SOLVENT FROM THE SAME END OF THE SYSTEM WHEREIN THE SOLVENT IS INTRODUCED, DISCHARGING AN EXTRACT FORMED BY THE SOLVENT, THE AROMATIC HYDROCARBONS AND A PORTION OF THE REFLUXING AGENT AND SUBSTANTIALLY FREE AND A PORTION OF THE REFLUXING AGENT AND SUBSTANTIALLY FREE OF THE NON-AROMATIC HYDROCARBONS FED-IN WITH THE HYDROCARBONACEOUS MIXTURE, SUBJECTING THE EXTRACT THUS OBTAINED TO WASHING WITHIN A COUNTERFLOW CONTACT SYSTEM WITH A LIGHT PARAFFIN FRACTION HAVING A BOILING POINT DEFINITELY LOWER THAN THAT OF THE AROMATIC HYDROCARBONS PRESENT IN THE EXTRACT, DISCHARGING FROM THE CONTACT SYSTEM IN WHICH THE WASHING IS CARRIED OUT A HEAVIER PHASE CONSISTING OF ALL THE SOLVENT AND SUBSTANTIALLY FREE OF HYDROCARBONS, AND DISCHARGING FROM THE OPPOSITE END OF A HYDROCARBONACEOUS PHASE CONSISTING OF THE SOLVENT-FREED AROMATIC HYDROCARBONS EXTRACTED FROM THE HYDROCARBONACEOUS MIXTURE AND LIGHT PARAFFIN HYDROCARBONS HAVING A BOILING POINT SUBSTANTIALLY LOWER THAN THAT OF THE MORE VOLATILE AROMATIC HYDROCARBON PRESENT IN THE SYSTEM, SEPARATING THE EXTRACTED AROMATIC HYDROCARBONS AND LIGHT PARAFFIN HYDROCARBONS HAVING A BOILING POINT SUBSTANTIALLY LOWER THAN THAT OF THE MORE VOLATILE AROMATIC HYDROCARBON PRESENT IN THE SYSTEM FROM THE SOLVENT-FREED EXTRACT BY EVAPORATION UNDER SUCH CONDITIONS AS TO EVOLVE THEREFROM A MAJOR ALIQUOT OF THE LOWBOILING LIGHT PARAFFIN FRACTION WHICH IS UTILIZED AS A REFLUXING AGENT AGAIN AND AS A WASHING AGENT, SEPARATING THEREAFTER FROM THE RESIDUAL EXTRACT THE REMAINDER OF THE LIGHT PARAFFIN FRACTION ALONG WITH A PORTION OF THE MORE VOLATILE AROMATIC HYDROCARBON AS A STREAM, MIXING SAID STREAM OBTAINED WITH THE FEED TO THE EXTRACTION SYSTEM AND NOT AS A REFLUX, AND OBTAINING AS A BOTTOM PRODUCT A HYDROCARBONACEOUS FRACTION CONSISTING OF SUBSTANTIALLY PURE AROMATIC HYDROCARBONS THE TEMPERATURE BEING MAINTAINED BETWEEN 20*C. AND 90*C. THROUGHOUT THE WHOLE PROCESS. 